A General Purpose Direct Current Ionization Chamber

Abstract

A large re-entrant ionization chamber which can take sources up to 15 in. (380 mm) long and 7 in. (178 mm) in diameter is described. It has been in use for several years and an account of its clinical and research applications is given. The input components are 10⁸ Ω, 10¹⁰ Ω and 100 μμF, and γ-emitting sources from a microcurie up to a curie can be measured to better than 1%. The detector is a vibrating reed electrometer used as a null indicator in conjunction with a voltage dividing box and all measurements are made by comparing the unknown source with three radium sources, one for each input range. The performance of the chamber with regard to accuracy and long term stability is described in detail and the paper includes some measured values of the half-lives of ¹³¹I, ¹³²I, ⁶⁰Co, ⁵⁹Fe, ¹⁸²Ta and ¹⁹⁸Au.